1. Genes within Populations

2. What is a population?
How are populations characterized?
What does it mean to be diploid, haploid, polyploid?
How can we characterize populations based on their genes?

3. What is a population?
A group of individuals of the same species that have a high potential of interbreeding
Share a common gene pool

4. Phenotype & Genotype
The phenotype is the expression of the genetic material (the genes) of the chromosomes.
The genotype relates to the alleles found at loci on the chromosomes

5. How many alleles can an individual have at a locus?
How many alleles can there be in a population at a specific locus?

6. Determining the genotype for an enzyme in a fish.

7. IDHP (isocitrate dehydrogenase) from a grasshopper
Individuals 1 2 3 AA Aa aa

8. Genotype There are 3 Genotypes  AA and aa (Homozygous), and
Aa (Heterozygous) there are 2 alleles A and a

9. Genotype frequency If there are 100 individuals 60 are AA 30 are Aa
Genotype frequency AA=60/100= Aa = 30/100= aa= 10/100 = Total = 1.0

10. Allele Frequency in 100 individuals there are 200 alleles
60 indiv. AA = 120 A
30 indiv. Aa = 30 A and 30 a
10 indiv. aa = 20 a
Therefore A = 150 A=150/200 = a = a=50/200 = 0.25

11. Phenotype there are 2 phenotypes trait “X” (AA and Aa) and
trait “Y” (aa)

12. Phenotype frequency
trait X = 90 indiv. (AA and Aa) trait Y = 10 indiv. (aa) Freq. X = 90/100 = Freq. Y =10/100 = 0.1

13. Hardy-Wienberg Equilibrium
If p = proportion of allele A and if q = proportion of allele a
Then p+q = 1
Hardy-Wienberg Equilibrium gives the expected frequency of the three genotypes as: (p+q)2 = p2 +2pq + q2 = 1
AA = p2, aa = q2 and Aa = 2pq

14. Hardy-Wienberg Equilibrium Assumptions
Population size is very large
Random mating is occurring
No mutation is taking place
No immigration (geneflow)‏
No selection is occurring

15. If the proportion of genotype aa in a population = 1% or 0.01
q2 = aa
Therefore q = square root of 0.01 =0.1
p= = 0.9
AA = p2 = 0.81
Aa = 2pq =0.18
aa = q2 = 0.010

17. How the Hardy-Wienberg Equilibrium can be used!

18. Extension to Hardy-Wienberg
Three alleles

20. Genotype frequency
p12 + 2p1p2 + 2p1p3 + p22 + 2p2p3 + p32 = 1

21. Populations share a common gene pool! What does this mean?
At each gene locus a population will be characterized by a particular allele frequency. The combination of allele frequencies is what characterizes a population and potentially makes populations unique.

22. What will cause deviation from Hardy-Wienberg Equilibrium?

23. Genetic Drift
For small populations random chance may result in the loss of an allele!
Results in Fixation
Loss of heterozygosity

24. Genetic drift is a random process

25. What is inbreeding and why is it bad?

26. Inbreeding
alleles are common by descent

27. Genes common by descent
Loss of heterozygosity
No loss of alleles

28. Other Processes
GENE FLOW – result of dispersal (an individual leaving one population and entering another population). Gene flow counters genetic drift.
FOUNDER EFFECT – refers to the chance gene combination in newly founded population (the variation in a new pop. Generally less than variation in the source population).
GENETIC BOTTLENECK – when a population is reduced to numbers but then recovers some genetic variation is generally lost.

30. What generalities and patterns are there?
Selection is a change in allele frequency
which is directional, NOT random.